Here's a non-exhaustive list of books and resources that really influence how we think about Octopus, and which you'll see reflected in this handbook. Reading these might give you further insight into why Octopus works the way it does.
Our thoughts around the roles of management at Octopus is influenced by High Output Management, and The Hard Thing About Hard Things. Scaling Up helped as we grew our management team, and Good Strategy/Bad Strategy along with Crossing The Chasm explains how we think about our strategy.
Much of our thinking around feedback comes from Radical Candour.
We are big fans of Basecamp. We use their Shape Up methodology, and their Handbook inspired us to finally write ours down. We look to companies like Redgate, JetBrains, and Atlassian as examples of companies we'd like to emulate.